The present invention relates to a method of treating tobacco to reduce the content of, or prevent formation of, harmful nitrosamines which are normally found in tobacco. The present invention also relates to tobacco products having low nitrosamine content.
Others have described the use of microwave energy to dry agricultural products. Use of microwave energy to cure tobacco is disclosed in U.S. Pat. No. 4,430,806 to Hopkins. In U.S. Pat. No. 4,898,189, Wochnowski teaches the use of microwaves to treat green tobacco in order to control moisture content in preparation for storage or shipping. In U.S. Pat. No. 3,699,976, microwave energy is described to kill insect infestation of tobacco. Moreover, techniques using impregnation of tobacco with inert organic liquids (U.S. Pat. No. 4,821,747) for the purposes of extracting expanded organic materials by a sluicing means have been disclosed wherein the mixture was exposed to microwave energy. In another embodiment, microwave energy is disclosed as the drying mechanism of extruded tobacco-containing material (U.S. Pat. No. 4,874,000). In U.S. Pat. No. 3,773,055, Stungis discloses the use of microwave to dry and expand cigarettes made with wet tobacco.
Prior attempts to reduce tar and harmful carcinogenic nitrosamines primarily have included the use of filters in smoking tobacco. In addition, attempts have been made to use additives to block the effects of harmful carcinogens in tobacco. These efforts have failed to reduce the oncologic morbidity associated with tobacco use. It is known that fresh-cut, green tobacco has virtually no nitrosamine carcinogens. See, e.g., Wiernik et al, xe2x80x9cEffect of Air-Curing on the Chemical Composition of Tobacco,xe2x80x9d Recent Advances in Tobacco Science, Vol. 21, pp. 39 et seq., Symposium Proceedings 49th Meeting Tobacco Chemists"" Research Conference, Sep. 24-27, 1995, Lexington, Ky. (hereinafter xe2x80x9cWiernik et alxe2x80x9d). However, cured tobacco is known to contain a number of nitrosamines, including the harmful carcinogens Nxe2x80x2-nitrosonornicotine (NNN) and 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK). It is widely accepted that such nitrosamines are formed post-harvest, during the curing process, as described further herein. Unfortunately, fresh-cut green tobacco is unsuitable for smoking or other consumption.
In 1993 and 1994, Burton et al at the University of Kentucky carried out certain experiments regarding tobacco-specific nitrosamines (TSNA), as reported in the Abstract, xe2x80x9cReduction of Nitrite-Nitrogen and Tobacco Nxe2x80x2-Specific Nitrosamines In Air-Cured Tobacco By Elevating Drying Temperaturesxe2x80x9d, Agronomy and Phytopathology Joint Meeting, CORESTA, Oxford 1995. Burton et al reported that drying harvested tobacco leaves for 24 hours at 71xc2x0 C., at various stages of air curing, including end of yellowing (EOY), EOY+3, EOY+5, etc. resulted in some reduction of nitrosamine levels. Reference is also made to freeze drying and microwaving of certain samples, without detail or results. Applicant has confirmed that in the actual work underlying this Abstract, carried out by Burton et al at the University of Kentucky, the microwave work was considered unsuccessful. Certain aspects of Burton et al""s 1993-94 study are reported in Wiernik et al, supra, at pages 54-57, under the heading xe2x80x9cModified Air-Curingxe2x80x9d. The Wiernik et al article postulates that subjecting tobacco leaf samples, taken at various stages of air-curing, to quick-drying at 70xc2x0 C. for 24 hours, would remove excess water and reduce the growth of microorganisms; hence, nitrite and tobacco-specific nitrosamine (TSNA) accumulation would be avoided. In Table II at page 56, Wiernik et al includes some of Burton et al""s summary data on lamina and midrib nitrite and TSNA contents in the KY160 and KY171 samples. Data from the freeze-drying and the quick-drying tests are included, but there is no mention of the microwaved samples. The article contains the following conclusion:
It can be concluded from this study that it may be possible to reduce nitrite levels and accumulation of TSNA in lamina and midrib by applying heat (70xc2x0 C.) to dark tobacco after loss of cell integrity in the leaf. Drying the tobacco leaf quickly at this stage of curing reduces the microbial activity that occurs during slow curing at ambient temperature. It must be added, however, that such a treatment lowers the quality of the tobacco leaf.
Id. at page 56. The Weirnik et al article also discusses traditional curing of Skroniowski tobacco in Poland as an example of a 2-step curing procedure. The article states that the tobacco is first air-cured and, when the lamina is yellow or brownish, the tobacco is heated to 65xc2x0 C. for two days in order to cure the stem. An analysis of tobacco produced in this manner showed that both the nitrite and the TSNA values were low, i.e., less than 10 micrograms per gram and 0.6-2.1 micrograms per grams, respectively. Weirnik et al theorized that these results were explainable due to the rapid heating which does not allow further bacterial growth. Weirnik et al also noted, however, that low nitrite and TSNA values, less than 15 micrograms per gram of nitrite and 0.2 microgram per gram of TSNA, were obtained for tobacco subjected to air-curing in Poland.
One object of the present invention is to substantially eliminate or reduce the content of nitrosamines in tobacco intended for smoking or consumption by other means.
Another object of the present invention is to reduce the carcinogenic potential of tobacco products, including cigarettes, cigars, chewing tobacco, snuff and tobacco-containing gum and lozenges.
Still another object of the present invention is to substantially eliminate or significantly reduce the amount of tobacco-specific nitrosamines, including Nxe2x80x2-nitrosonornicotine (NNN), 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK), Nxe2x80x2-nitrosoanatabine (NAT) and Nxe2x80x2-nitrosoanabasine (NAB), in such tobacco products.
Another object of the present invention is to treat uncured tobacco at an appropriate time post-harvest so as to arrest the curing process without adversely affecting the tobacco""s suitability for human consumption.
Another object of the present invention is to reduce the content of tobacco-specific nitrosamines in fully cured tobacco.
The above and other objects and advantages in accordance with the present invention can be obtained by a process for reducing the amount of or preventing formation of nitrosamines in a harvested tobacco plant, comprising
subjecting at least a portion of the plant to microwave radiation, while said portion is uncured and in a state susceptible to having the amount of nitrosamines reduced or formation of nitrosamines arrested, for a sufficient time to reduce the amount of or substantially prevent formation of at least one nitrosamine.
It is preferred that in the process of the invention, the step of subjecting to microwave radiation is carried out on a tobacco leaf or portion thereof after onset of yellowing in the leaf and prior to substantial accumulation of tobacco-specific nitrosamines in the leaf.
It is also preferred that in the process of the invention, the step of subjecting to microwave radiation is carried out prior to substantial loss of the leaf""s cellular integrity.
In additional preferred embodiments of the process, the tobacco is flue tobacco and the step of subjecting to microwave radiation is carried out within about 24 to about 72 hours post-harvest, even more preferably within about 24 to about 36 hours post-harvest.
In still other embodiments of the process, the harvested tobacco is maintained under above-ambient temperature conditions in a controlled environment prior to the step of subjecting to microwave radiation.
Preferred aspects of the process include a step, prior to subjecting a tobacco leaf which preferably includes the stem to microwave radiation, of physically pressing the leaf to squeeze excess moisture therefrom, to ensure more uniform drying by the microwave unit. This step can be conveniently carried out by passing the leaf through a pair of appropriately spaced rotating cylindrical rollers prior to entering the microwave cavity.
In yet additional preferred embodiments of the invention, the microwave radiation has a frequency of about 900 to about 2500 MHz, and is applied to the plant for a period of at least about 1 second, and preferably from about 10 seconds to about 5 minutes at a predetermined power level. The power level used generally determines the length of time to which the tobacco is subjected to the microwave radiation, and can range from about 600 to about 1000 watts when using conventional kitchen-type microwave ovens, up to several hundred or more kilowatts for commercial, multimode applicators. Preferred power levels using applicators designed to handle single leaves range from about 2 to about 75 kilowatts, more preferably from about 5 to about 50 kilowatts, which permit relatively rapid treatment to be carried out.
It is also preferred in accordance with the present invention that the microwave radiation is applied to the leaf or portion thereof for a time sufficient to effectively dry the leaf, without charring, so that it is suitable for human consumption.
The present invention also seeks to subject tobacco leaves to microwave radiation to prevent normal accumulation of at least one tobacco-specific nitrosamine, such as Nxe2x80x2-nitrosonornicotine, 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone, Nxe2x80x2-nitrosoanatabine and Nxe2x80x2-nitrosoanabasine.
The present invention in its broadest forms also encompasses a tobacco product comprising non-green tobacco suitable for human consumption and having a lower content of at least one tobacco-specific nitrosamine than conventionally cured tobacco.
In preferred embodiments, the non-green tobacco product has a TSNA (NNN, NNK, NAB and NAT) content of less than 0.2 xcexcg/g, more preferably less than about 0.15 xcexcg/g, and even more preferably less than about 0.1 xcexcg/g, an NNN content of less than about 0.15 xcexcg/g, more preferably less than about 0.10 xcexcg/g, and even more preferably less than about 0.05 xcexcg/g, and an NNK content of less than about 0.002 xcexcg/g, more preferably less than about 0.001 xcexcg/g, and even more preferably less than about 0.0005 xcexcg/g.
The present invention is also directed to a tobacco product comprising dried yellow tobacco suitable for human consumption and having a lower content of at least one tobacco-specific nitrosamine than conventionally cured tobacco. In preferred embodiments, the yellow tobacco product has a TSNA (NNN, NNK, NAB and NAT) content, an NNN content, and an NNK content within the above preferred ranges.
In other embodiments, the non-green or yellow tobacco product comprises non-green or yellow tobacco suitable for human consumption, and having a TSNA (NNN, NNK, NAB and NAT) content within about 25% by weight of the content of such TSNA in the freshly harvested green tobacco crop from which the product was made. It is more preferred that the non-green or yellow tobacco product have a TSNA content within about 10% by weight, more preferably within about 5% by weight and most preferably essentially approximating (e.g. within an amount up to several, percent by weight) the content of such TSNA in the freshly harvested tobacco crop from which the product was made. It is also preferred that the non-green or yellow tobacco product comprises non-green or yellow tobacco suitable for human consumption, and having content of at least one TSNA selected from NNN, NNK, NAB and NAT, which is within about 25% by weight, preferably within about 10% by weight, more preferably within about 5% by weight and most preferably essentially approximating (e.g. within an amount up to several percent by weight) of the content of the corresponding TSNA or TSNAs in the freshly harvested green tobacco crop from which the product was made.
In yet additional embodiments of the invention, the non-green or yellow tobacco product comprises non-green or yellow tobacco suitable for human consumption, and having a TSNA (NNN, NNK, NAB and NAT) content which is at least about 75% by weight, preferably at least about 90% by weight, more preferably at least about 95% by weight, and most preferably at least about 99% by weight lower than the content of such TSNA in a tobacco product of the same type made; from the same tobacco crop as the product of the invention, but which was cured in the absence of microwave radiation or other techniques designed to reduce TSNA content. It is also preferred that the non-green or yellow tobacco product comprises non-green or yellow tobacco suitable for human consumption, and having a content of at least one TSNA selected from NNN, NNK, NAB and NAT which is at least about 75% by weight, preferably at least about 90% by weight, more preferably at least about 95% by weight, and most preferably at least about 99% by weight lower than the content of the corresponding TSNA or TSNAs in a tobacco product of the same type made from the same tobacco crop as the product of the invention, but which was cured in the absence of microwave radiation or other techniques designed to reduce TSNA content.
A preferred form of the present invention relates to a tobacco product comprising tobacco having a reduced content of at least one tobacco-specific nitrosamine, produced by a process comprising subjecting the tobacco, while the tobacco is uncured and susceptible to having formation of at least one tobacco-specific nitrosamine arrested, to microwave radiation.
In another embodiment, the present invention is directed to a method for reducing the content of at least one tobacco-specific nitrosamine in cured brown tobacco, comprising
rehydrating the cured brown tobacco, and
subjecting the rehydrated tobacco to microwave radiation at a predetermined energy level for a predetermined length of time.
Similarly, the present invention includes within its scope a tobacco product comprising cured brown tobacco having a reduced content of at least one tobacco-specific nitrosamine, produced by a process comprising
rehydrating the cured brown tobacco, and
subjecting the rehydrated tobacco to microwave radiation at a predetermined energy level for a predetermined length of time.
In yet another embodiment, the present invention relates to a method of manufacturing a tobacco product, comprising
subjecting harvested tobacco leaves to microwave radiation, while said leaves are uncured and in a state susceptible to having the amount of tobacco-specific nitrosamines reduced or formation of tobacco-specific nitrosamines arrested, for a sufficient time to reduce the amount of or substantially prevent formation of at least one tobacco-specific nitrosamine in the leaves, and
forming the tobacco product comprising the microwaved leaves, the tobacco product being selected from cigarettes, cigars, chewing tobacco, snuff and tobacco-containing gum and lozenges.